Viruses, Bacteria & Diseases

VirusesViruses are NOT cells. A virus is an infectious agent made up of:

•a core of nucleic acid (RNA or DNA)

•a protein coat (capsid)

•Genetic material carries information for multiplication

•Hijacks biochemical machinery of host cell to carry these processes out•So…viruses are NOT LIVING

CELLCELL VIRUSVIRUS

Made of cells YES NO

Obtain & use energy

YES NO

Grow & develop

YESOnly inside a living cell

Reproduce YESOnly inside a living cell

Respond & adapt

YES YES

Contain RNA or DNA

YES YES

Characteristics

of life

Re-CapViruses are NOT ALIVE. Viruses do not:•Grow

•Have homeostasis

•Metabolize

Viruses do:•Infect cells and use the cell to make more

viruses

•Cause disease in many organisms

Structureof a virus• Envelope (part of

the protein coat)• Capsid (part of

the protein coat)• Nucleic acid

(either DNA or RNA)

ENVELOPE

NUCLEIC

ACIDCAPSID

Retrovirus• A virus that

contains RNA instead of DNA

• Human Immunodeficiency Virus (HIV) is a retrovirus

• HIV causes AIDS

ENVELOPE

RNA

CAPSID

Bacteriophage• A virus that

only infects bacteria

CAPSID

DNA

TAIL FIBER

HEAD

CAPSID

Ticking time bombs . . .

Viruses do not reproduce by themselves. They invade a living cell and let the cell do the work for them.

Lytic CycleThe viral infection that rapidly kills the host cell is the lytic cycle.

1 2 3

4 5

Cycle Illustration

Lysogenic Cycle

The viral infection that enters a cell, remains harmless for a period of time (sometimes years), and then becomes harmful later is called the lysogenic cycle.

In the lysogenic cycle, the virus reproduces by first injecting its genetic material, indicated by the red line, into the host cell's genetic instructions.

Lysogenic Cycle

Role of viruses

• All viruses act like parasites, harming the host cell.

• Viruses cause disease in every kind of organism—animals, plants, fungi, protists, and bacteria.

• HIV• Measles• Smallpox• Influenza• Chicken pox

• Common cold• Herpes• Warts• Mononucleosi

s• Mumps

Some viral diseases

HIV• A retrovirus• Infects human helper T-cells, which

are associated with the immune system.

• Modes of transmission: – Sexual contact with an infected person– Sharing needles with an infected person– Blood transfusions (rare)– Breast feeding– Etc.

HPV• Human Papilloma Virus• Causes warts• Most common STD in the United

States• 80% of women by the age of 50 will

have acquired some strain of genital HPV.

• HPV vaccine

Influenza (flu)• Symptoms: body aches, fever,

coughing, runny nose, fatigue, usually lasting about a week.

• Mode of transmission– Airborne (air droplets)

People still die from influenza.

usually cannot be cured, but many can be prevented by

•Good hygiene•Immunization

Viral diseases

Bacteria

Bacteria are Prokaryotes.

Prokaryotic Cells:• Have no nucleus• Do not have membrane

bound organelles• Are very small• Often have a flagellum

for movement

Shapes of bacteria

Bacteria are classified according to their shape:

• Round is called cocci

• Rod shaped is called bacilla

• Spiral shaped is called spirilla

Where do they live?

• Bacteria are found in all environments

Role of bacteria• Some bacteria are helpful

– E. coli– Yeast– V.streptococci– Lactobacillus

• Some bacteria are harmful– E. coli– S. pyogenes– S. aureus– Y. pestis

Streptococcus

• Causes strep throat, pneumonia, and other infections.

• Named based on the shape and orientation of the bacteria.

Staphylococcus • Cause of staph infections that occur

on the skin or in wounds. (ex. MRSA)

• But, Certain types of staph reside normally on the skin.

Diphtheria• Swelling of the upper respiratory tract

• DPT Vaccine

• Can also infect skin cells.

•How do bacteria cause disease?–The release toxins that interfere with normal activity.

Prevention/Cure

•Vaccines to prevent.

•Antibiotics to cure (pennicillin, amoxycillin, etc).